1. Field of the invention
The present invention relates to an information reproducing system for reading out information from an optical recording medium such as an optical disk which has a plurality of storage layers parallel to its plane.
2. Discussion of the Prior Art
An optical disk having a plurality of information storage layers is known to improve the density of information stored per unit area of the disk. For example, Laid-open Publication No. 61-107552 (published on May 26, 1986) of Japanese Patent Application No. 59-228743 proposes a magneto-optical disk which has a plurality of magneto-optical storage layers. The subject matter of the above-identified Japanese Patent Application is disclosed in U.S. patent application Ser. No. 792 591 filed Oct. 29, 1985, assigned to the assignee of the present application. According to this magneto-optical disk, information may be written on and read from the individual magneto-optical storage layers, whereby the density of information recordable per unit area of the disk is drastically increased.
However, a conventional optical disk having two or more storage layers as indicated above requires corresponding light sources for emitting laser beams having different wavelengths for reading recorded information from the respective storage layers, respectively. Further, this conventional system requires two or more sets of detectors adapted to the different wavelengths of the laser beams reflected by the respective storage layers, so that the information can be read based on a change in the Kerr rotation angles of the reflected beams having the different wavelengths. Hence, the conventional information reading or reproducing system tends to be complicated in construction and expensive.